The present invention relates to methods of forming a face plate assembly of a color display.
Field emission displays and cathode ray tubes are types of color displays which can function by having a layer of phosphor-comprising material applied on an internal surface of a face plate known as an anode, cathodeluminescent screen, display screen, or display electrode. Color displays typically include three different types of phosphor, namely red, green, and blue (RGB), which, when excited in various combinations, produce colors for presentation through the face plate of the display. The phosphor-comprising material is typically oriented or arranged in a series of pixels. Pixels are typically discrete areas of phosphor-comprising material formed on the internal surface of the face plate.
A technique by which such areas are provided on a face plate involves the use of photolithographic techniques to pattern the phosphor-comprising material. Typically, a faceplate will be coated with a thin layer of conductive material, generally Indium Tin Oxide (ITO). This conductive layer of material is coated with a layer of photoresist, which in turn, is used to pattern phosphor-comprising material into a color array of pixels. It may also serve for patterning black matrix material into a pixel pattern. Black matrix material is used in order to give greater contrast in color displays. Pixels, or holes, will be opened up in the photoresist using photolithographic techniques, thereby exposing distinct regions of the conductive material. The photolithographic techniques used to open the pixels or holes in the photoresist typically involve the use of developer solutions. For negative resists, developer solutions selectively dissolve and remove regions of the photoresist that have not been exposed to radiation actinic to the photoresist used. The black matrix and phosphor-comprising materials can then be electrophoretically deposited into the holes opened in the photoresist. The conductive layer is used as an electrode for depositing phosphor-comprising materials through electrophoresis. Electrophoresis, or electrophoretic deposition, in simply the migration of charged particles through a solution under the influence of an applied electric field applied by immersing two electrodes in the solution. Exemplary methods of depositing black matrix material and phosphor-comprising material are described in U.S. Pat. No. 4,891,110, the disclosure of which is incorporated by reference. Exemplary color displays are described in U.S. Pat. Nos. 5,712,534, 5,705,079, 5,697,825 and 5,688,438, the disclosures of which are incorporated by reference.
Photolithographic color patterning of a display typically involves the use of incident radiation, photomasks, and wet-chemical developers to selectively expose various pixels for deposition of black matrix material and different colors of phosphor-comprising material therein. Despite the use of these developers, electrophoretic deposition of powdered materials such as manganese carbonate and phosphor-comprising material can result in trace deposits undesirably remaining over adjacent areas or pixels. Such trace deposits can result in black spots and color cross-contamination with undesired color phosphor remaining in adjacent pixels dedicated to other colors, thus leading to color bleed and a less desirable display.
This invention arose out of concerns associated with improving the methods by which phosphor-comprising material is formed over face plates of color displays. This invention also arose out of concerns associated with providing improved color displays.
Methods of forming face plate assemblies are described. In one implementation, a substrate is patterned with photoresist and a first phosphor-comprising material is formed over first surface areas of the substrate. The photoresist is stripped leaving some of the first phosphor-comprising material over substrate areas other than the first areas. Photoresist is again formed over the substrate and processed to expose second substrate areas which are different from the first substrate areas. In a preferred aspect, processing the photoresist comprises using a heated aqueous developing solution comprising an acid, e.g. lactic acid, effective to dislodge and remove first phosphor-comprising material from beneath the developed photoresist. A second phosphor-comprising material is formed over the substrate and the exposed second areas, with trace deposits being left over other substrate areas. The photoresist is subsequently stripped leaving some of the second phosphor-comprising-:material over substrate areas other than the first and second areas. Photoresist is again formed over the substrate and processed to expose third substrate areas which are different from the first and second areas. In a preferred aspect, processing the photoresist comprises using a heated aqueous developing solution comprising an acid, e.g. lactic acid, effective to dislodge and remove first and second phosphor-comprising material from beneath the removed photoresist. A third phosphor-comprising material is formed over the substrate and the exposed third areas.